PHP 8.2 新特性之 Readonly Class （只读类）
PHP 8.1 添加了只读属性，只读属性只能设置一次。
PHP 8.2 对只读属性做了一次升级，那就是声明 Readonly Class。一个类一旦被设置为只读类，那么这个类中的属性都是只读属性。
PHP8.2
1、基础使用
只读类使用关键字 readonly 标记。
<span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(86, 182, 194) !important"><?</span><span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">php</span></span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"><span style="box-sizing: border-box"></span></span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(98, 151, 85) !important">// 只读类</span></span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">readonly</span> <span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">class</span> <span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">WebSite</span></span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px">{</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"> <span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">public</span> <span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">function</span> <span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">__construct</span>(<span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">public</span> <span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">string</span> <span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">$webName</span> <span style="box-sizing: border-box;color: rgb(86, 182, 194) !important">=</span> <span style="box-sizing: border-box;color: rgb(152, 195, 121) !important">''</span>, <span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">public</span> <span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">string</span> <span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">$webUrl</span> <span style="box-sizing: border-box;color: rgb(86, 182, 194) !important">=</span> <span style="box-sizing: border-box;color: rgb(152, 195, 121) !important">''</span>)</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"> {</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"> }</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px">}</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">$webSite</span> <span style="box-sizing: border-box;color: rgb(86, 182, 194) !important">=</span> <span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">new</span> <span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">WebSite</span>(<span style="box-sizing: border-box;color: rgb(152, 195, 121) !important">'自如初'</span>, <span style="box-sizing: border-box;color: rgb(152, 195, 121) !important">'www.ziruchu.com'</span>);</span>
若对只读属性赋值，则会报错，如下：
<span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(98, 151, 85) !important">// 为只读属性赋值，会报错</span></span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">$webName</span><span style="box-sizing: border-box;color: rgb(86, 182, 194) !important">-></span><span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">webName</span> <span style="box-sizing: border-box;color: rgb(86, 182, 194) !important">=</span> <span style="box-sizing: border-box;color: rgb(152, 195, 121) !important">'PHP'</span>;</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(98, 151, 85) !important">// 报错信息如下</span></span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">PHP</span> <span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">Fatal</span> <span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">error</span>: <span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">Uncaught</span> <span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">Error</span>: <span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">Attempt</span> <span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">to</span> <span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">assign</span> <span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">property</span> <span style="box-sizing: border-box;color: rgb(152, 195, 121) !important">"webName"</span> <span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">on</span> <span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">null</span> <span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">in</span></span>
2、 只读抽象类与继承
<span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(86, 182, 194) !important"><?</span><span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">php</span></span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"> </span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">readonly</span> <span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">abstract</span> <span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">class</span> <span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">Animal</span></span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px">{</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"> <span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">public</span> <span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">string</span> <span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">$name</span>;</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px">}</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"><span style="box-sizing: border-box"></span></span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">readonly</span> <span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">class</span> <span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">Cat</span> <span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">extends</span> <span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">Animal</span></span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px">{</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"> <span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">public</span> <span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">function</span> <span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">__construct</span>(<span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">public</span> <span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">string</span> <span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">$name</span>)</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"> {</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"> }</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"><span style="box-sizing: border-box"></span></span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"> <span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">public</span> <span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">function</span> <span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">getName</span>()</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"> {</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"> <span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">echo</span> <span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">$this</span><span style="box-sizing: border-box;color: rgb(86, 182, 194) !important">-></span><span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">name</span>;</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"> }</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px">}</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"><span style="box-sizing: border-box"></span></span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">$cat</span> <span style="box-sizing: border-box;color: rgb(86, 182, 194) !important">=</span> <span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">new</span> <span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">Cat</span>(<span style="box-sizing: border-box;color: rgb(152, 195, 121) !important">'花花'</span>);</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">$cat</span><span style="box-sizing: border-box;color: rgb(86, 182, 194) !important">-></span><span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">getName</span>();</span>
3、关于接口
错误案例
<span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(86, 182, 194) !important"><?</span><span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">php</span></span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(98, 151, 85) !important">// 错误，接口不能设置为 readonly</span></span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">readonly</span> <span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">interface</span> <span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">Animal</span></span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px">{</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"> <span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">public</span> <span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">function</span> <span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">getName</span>();</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px">}</span>
正确案例
<span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">interface</span> <span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">Animal</span></span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px">{</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"> <span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">public</span> <span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">function</span> <span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">getName</span>();</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px">}</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"><span style="box-sizing: border-box"></span></span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"> <span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">class</span> <span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">Dog</span> <span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">implements</span> <span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">Animal</span></span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px">{</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"> <span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">public</span> <span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">function</span> <span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">__construct</span>(<span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">public</span> <span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">string</span> <span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">$name</span>)</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"> {</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"> }</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"><span style="box-sizing: border-box"></span></span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"> <span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">public</span> <span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">function</span> <span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">getName</span>()</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"> {</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"> <span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">echo</span> <span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">$this</span><span style="box-sizing: border-box;color: rgb(86, 182, 194) !important">-></span><span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">name</span>;</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"> }</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px">}</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"><span style="box-sizing: border-box"></span></span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">$dog</span> <span style="box-sizing: border-box;color: rgb(86, 182, 194) !important">=</span> <span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">new</span> <span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">Dog</span>(<span style="box-sizing: border-box;color: rgb(152, 195, 121) !important">'旺财'</span>);</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">$dog</span><span style="box-sizing: border-box;color: rgb(86, 182, 194) !important">-></span><span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">getName</span>();</span>
readonly class 特性：
- 只读属性只能进行第一次赋值，再次赋值则会报错；
- 抽象类可以设置为只读类；
- 接口不能设置为只读类，但其实现者可以设置为只读类；
- trait 不能设置为只读类
关于 PHP 8.2 Readonly Class 的使用，我们一切发掘。
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